In high speed (e.g., 10 giga bits per second (Gb/s)), high performance, serial communication receivers that require equalization, VGA and CTF are sometimes used on the front end of the topology. The VGA is used to either provide gain or attenuation depending on the amplitude of the input signal such that the VGA will output a substantially constant amplitude signal. The ability to adjust the gain/attenuation of the VGA so that both a very large and very small input voltage swing range at the input to the receiver can be accommodated is desirable for 10 Gb/s serial data communication applications.
Depending on the application, there are situations in which the minimum and maximum input swing range is so large that it is difficult to provide a VGA to cover the whole input dynamic range. Further, even when such a large input swing range can be covered, a total harmonic distortion (THD) of the VGA may not be adequate over at least some of the range, because of non-linearity of the gain. Therefore, it is desirable to design a VGA that accommodates a large input dynamic range while THD is kept at a low value. Further, it is desirable to reduce die areas and power for the VGA and CTF circuits.